Thermal Allometry and Massive Architecture

Jerónimo van Schendel
Aaron Mendonca
Sarah Kantrowitz

Architects deal with thermodynamics-related problems in ways that tend to be intuitive, lacking quantitative correlations between design decisions and energy performance, which poses a barrier to integrating thermal mass and natural ventilation into contemporary construction.

To break this barrier, the architects and postgraduate students Jerónimo van Schendel, Aaron Mendonca, and Sarh Kantrowitz, under the direction of the specialist in architectural thermodynamics Salmaan Craig, all of them from Harvard GSD, have contributed to the development of a model that studies the allometric relations which make it possible to ‘tune’ any space to resonate with daily or seasonal temperature swings. Understanding such a geometric approach and its relationship with the material character of architecture is key to making informed design decisions that translate into spaces activated by thermal masses.

There are fascinating and successful examples of these phenomena in nature. H. King, S. Ocko, and L. Mahadevan have recently studied the mechanism of natural ventilation that regulates temperature in termite mounds. Salmaan Craig explains how by form and ‘massing’ alone, as in an orchestra, termite mounds balance the baritone beat of thermal mass with the soprano shrill of surface convections and the tenor pulse of buoyancy ventilation. The mound stays cool and fresh as the synchrony of thermal effects plays on. In thermodynamic terms, the mound extracts work from the daily and nightly temperature oscillations. It resonates – at perfect pitch – with phenomena that occur around it on different spatial and temporal scales.

If buildings today approach this kind of thermal resonance, it has more to do with happenstance than with design. For all the history of architecture built with earth, masonry and concrete, we still cannot tune our buildings to the beat of their environments well enough to offer serious alternatives to air-conditioning. Many basic questions remain unanswered. What geometries, what dimensions, what configurations, what relationships are the right ones, and how do they vary with scale?

Allometry, a term borrowed from biology, describes how the characteristics of living things change with size. The study of thermal allometry in architecture concerns itself with the mechanisms, in it, of form, material, thermal oscillation, and ventilation, and with their variations with changes in scale.

In this experimental study, Salmaan Craig’s theory has been put to the test. The study proposes an architectural interior in resonance with the environment that is at the same time able to lightly condition some exterior spaces by generating and channeling a soft breeze. An initial space, the ‘House’, is transformed into its amplified version, the ‘Palace.’ The transformation endeavors to maintain the balance between all the above-mentioned variables, at both scales. To push buoyancy ventilation beyond just regulating interior temperature and to further explore the range of experiential delights that thermodynamics can bring to architecture, the designs are centered on courtyards and balcony spaces, the main beneficiaries of the breezes generated inside buildings.

The photographs that accompany this text show the water baths that were designed to observe and prove the ability of the ‘House’ and ‘Palace’ morphologies to generate internal ventilation and breezes outside buildings. Each bath represents the smallest possible unit, with a different configuration. In the case of the ‘House,’ it is a section of the courtyard; in that of the ‘Palace,’ a succession of three floors. Introduced into the water baths are models of methacrylate and plates of hot steel, with all the physical variables on scale, using black ink to visualize the natural flows generated, which can hence be observed in a way that is both efficient and intuitive.

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